Quote:
Originally Posted by
Beekey (Post 204550)
I have also noticed that the surging has been worse lately. I suspect its because the air temp over last few days have been around 0 degrees Celcius. Would that be right? Anyway, when the wife isn't looking at my bank balance I will be getting the O2 controller to hopefully fix this issue once and for all.
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Quote:
Originally Posted by
Beekey (Post 204566)
Hmmmm, today was around 9 degrees C and the surging was definitely less on exactly the same commute. I would say the cold air does make quite a difference. Looking forward to seeing how the O2 controller deals with this.
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The way the Kev mod works means its ability to adjust fuelling (A/F ratio) will be affected to some degree by changes in ambient temperature. The fact that you feel the surging returning as the outside temperature falls is nothing out of the ordinary. What you need to do is compensate by increasing the resistance (turning the knob further in a clockwise direction) when the weather is cold. I�ll try and explain what�s going on with getting too boring and delving into the physics of it all�
The Kev mod works by artificially increasing the resistance of the air intake temperature (AIT) sensor to kid the ECU into thinking it�s colder than it actually is, thereby causing the ECU to decrease the air/fuel ratio (make it richer). The resistance of the Kev mod is added in series with that of the AIT sensor. Whatever additional resistance you dial in stays fixed, whereas the resistance of the AIT sensor varies, increasing as the ambient temperature falls. The issue you are noticing arises because the extra resistance you dialled in is proportionally greater part of the total resistance at higher ambient temperatures, when the AIT sensor has a low internal resistance. As the AIT resistance increases (as air temperature falls), your setting on the Kev mod becomes proportionally less � in other words, it will have less effect on the A/F ratio and the same setting will give a weaker mixture.
If we put some numbers into the mix it might help explain things better? (BTW - The numbers aren�t the real ones, I�ve just chosen them to help make the maths easy and to exaggerate what�s going on.)
Let�s say your mod is set to 5K, it is 20C outside and the AIT sensor�s resistance is 100K, the result is you have increased the resistance by 5%. Keep the setting at 5K, let�s say the air temperature drops to 0C and the AIT sensor�s resistance rises to 200K, the net result is an increase in resistance of just 2.5%. As you can see from the figures, the same setting will not have the same effects at 0C as it will do at 20C. Therefore any given base setting on the mod will produce a progressively weakening mixture as air temperature falls; conversely the mixture will become richer as the temperature rises. All Kev�s fuelling mods are tested at 20C and so the suggested settings only apply at that ambient temperature; they are a guide. Any deviation from 20C ambient will require adjustment to compensate.
This graph illustrates what�s happening. You can easily see how the two lines converge as the temperature falls.
http://i864.photobucket.com/albums/a...psc1af2c35.jpg
In real life it�s not quite as extreme as my illustration thankfully, so a moderate change in setting is all that�s needed. I found that for UK summer riding (generally around 20C) Kev�s suggested settings were fine. Below 10C I increased the setting on the knob by one increment (say from 4 o�clock to 5 o�clock), and below 0C the bike needed +2 over base to achieve the same results as in the summer (moving from 5 to 6 o�clock).
Fitting an O2 controller will also help quite a lot, because the main cause of the surging is the sudden step from closed loop fuelling to open loop fuelling and vice-versa. This step is exaggerated as ambient temperature falls and the mixture weakens due to the Kev mod having less influence on the fuelling. By fixing the closed loop at 13.6:1 with the O2 controller this �step� is all but eliminated.
